1. Field of the Invention
This invention relates in general to the field of bubble memory devices, and in particular to bubble memory devices of the lattice type.
2. Description of the Prior Art
In magnetic bubble lattice devices wherein information is stored in the domain wall structure of the bubble, the two information states representing "1" and "0" are represented by the presence or absence of a pair of Bloch lines. For purposes of this discussion, Bloch lines may be defined as a transition zone through which the magnetization at the center of the domain wall reverses direction. For reliable information storage, both states must be equally stable.
In conventional prior art bubble lattice devices such as disclosed in U.S. 3,996,577 magnetic garnet films are grown on oriented substrates and are ion implanted (i.e., the film surface has been bombarded and implanted with ions). In such films, only one stable information state can be obtained. In order to obtain the second information state, an appropriate external in-plane field must be applied. The presence of the in-plane field has the effect of stabilizing this second information state without destroying the first state. If the in-plane field were not present, one information state would be overwhelmingly more stable than the other state.
The requirement of an external in-plane field is an undesirable characteristic of the known prior bubble lattice devices since it requires additional fabrication steps or hardware. This results from the facts that additional conductors must be deposited on the substrate or a set of external field coils must be included. The conductor or external coils are an added cost because of the additional circuitry required to be connected thereto in order to energize it at the proper time.